The present invention relates to improvements in a method and apparatus for evaluating discrete portions of information on web-like carriers of information, especially for evaluating successive film frames on a web of spliced-together exposed and developed photographic color films prior to reproduction of the images of film frames in a copying machine. More particularly, the invention relates to a method and apparatus for producing density, color correction and/or other signals for transmission to the exposure controls of a copying machine in order to insure proper adjustment of exposure controls during reproduction of the respective film frames.
In accordance with a presently known procedure, an attendant examines successive frames of a web of photographic color films in order to detect those frames whose copying must be carried out with special adjustment of exposure controls in the copying machine. In the absence of any special adjustment, the exposure controls will cause the copying machine to make prints with an average density and with a tonal distribution which results in neutral grey on integral measurement of the entire film frame. In most instances, such method of examining and reproducing color film frames results in the making of acceptable color prints. However, the prints are unsatisfactory if the density distribution is not uniform or nearly uniform in all portions of a film frame and/or when a primary color dominates, e.g., because the photographer selected for exposure a scene the major part of which is blue, green or red. Automatic determination of the setting of exposure controls for reproduction of such film frames would entail undesirable suppression of dominant color and/or undesirable density of the most important part of the print.
It is further known to subject successive film frames to an automatic objective evaluation. As disclosed, for example, in commonly owned U.S. Pat. No. 3,523,728 to R. Wick et al., each frame can be subdivided into three imaginary sections or fields including a first field which coincides with the foreground of the photographed scene, a second field which coincides with the background of the scene, and a third field which coincides with the center of the scene and normally constitutes the most important part of the scene. The automatic evaluating system examines the three fields independently of each other and normally or often suppresses correction signals which are produced on examination of the first two fields in order to insure proper reproduction of the third field, i.e., of the most important part of the photographed scene. As a rule, the first field is in the lower part of the frame, the second field is in the upper part of the frame and the third field is in the middle of the frame. The just discussed breakdown of film frames into three fields is especially satisfactory for proper selection of adjustment of exposure controls to insure an optimum density of the prints.
A presently known determination of color correction factors is carried out primarily with a view to discriminate between film frames wth a dominant color and film frames with an undesirable color shade. Such determination normally involves a statistical evaluation of color ratios, i.e., the frame is scanned point-by-point and each point wherein a color prevails is classified as belonging to a dominant color. Such points are not considered in selection of exposure times for the particular color. In accordance with another presently known method, one determines the color ratio in a large number of frames forming part of a film; this allows for selection of appropriate adjustment of exposure controls to eliminate an undesirable color shade. Of course, such mode of examining film frames for the purpose of proper exposure in three colors does not take into consideration the possibility that a large number of film frames might carry the image of one and the same scene; in such instances, the presently known procedure of discriminating between the presence of a dominant color and a color shade is evidently ineffective.
Additional problems are encountered when the frames of a color photographic film include one or more frames with a density distribution which is basically different from the density distribution in an average film frame. Examples of such film frames are those which are exposed with flash; such frames invariably exhibit a poorly illuminated background which surrounds a strongly illuminated central field normally representing the images of a group of persons and being by far the most important part of the image. When making a print of such frame, the exposure controls of the copying machine must be properly adjusted to avoid an underexposure of the important field.
Further problems in connection with proper evaluation of film frames prior to copying will arise due to orientation of images on the frames. Thus, when an automatic prereader is set for separate scanning of the foreground, the background and the central field of a film frame, the prereader cannot determine whether or not the frame was exposed with the camera held at right angles to the normal position or upside down. A photographer is less likely to change the orientation of his or her camera when the film contains square frames. However, the likelihood that the photographer will tilt the camera, or even hold the camera upside down, is much more pronounced when the film consists of rectangular frames. As mentioned above, an automatic prereader cannot discriminate between a rectangular frame which bears a properly oriented image and a rectangular frame whereon the image is inclined through 90.degree. or 180.degree. with respect to the anticipated normal orientation of images. Therefore, correction signals which are produced by an automatic prereader upon evaluation of frames having improperly oriented images (whereby the term "improperly" denotes images whose orientation is different from anticipated orientation) will be unsatisfactory and the corresponding film frame will have to be reprinted in order to avoid customer complaints. A prereader which can compensate for improper orientation of images on film frames is disclosed in the commonly owned copending application Ser. No. 739,548 of Betzold et al. filed Nov. 8, 1976 now U.S. Pat. No. 4,080,066.